1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to the electrical storage and supply system for providing electrical power to an electrical motor.
2. Description of the Related Art
In the mining equipment market, DC motors for scoops and coal haulers are typically rated at 110, 120 or 128 volts. For the past 50 years, battery operated DC wound motors have been rated at 128 volts or lower in their electrical operating systems. In past, it was typical for 128 volt battery systems to supply power to an electric motor rated as 128 volts. With some improvements in motor technology, more power could be generated such that an electrical motor rated at 110 volts could replace the electric motors rated at 128 volts. In order to permit replacement of the 128 volt motors with 110 volt motors, choppers were used to drop the battery packs 128 volt supply to 110 volts. This prevented equipment owners from having to replace their 128 volt battery packs with 110 volt battery packs.
Industrial batteries that are used in the mining industry provide power for underground mining equipment. DC (direct current) power is a chemical process to make electricity, for example, in one configuration positive and negative lead plates are submerged in an acid and water bath known as electrolyte. This process creates the electricity that powers the machines underground. The plates are typically encased in plastic jars and rated at 2 volts per cell which is one plastic jar. When fully charged, however, each cell will generate 2.15 to 2.17 volts. Because the output voltage of the battery varies as it is discharged, a standard is used. The industry standard is to assume 2 volts per cell and that is how the industry routinely measures the size of the battery tray. For example, a 64 cell battery would be referred to as a 128 volt battery, although at full charge the battery may output in excess of 130 volts. A battery tray usually consists of 64 cells but some machines require different numbers of cells, such as 24, 48, and 60.
Typically, the industry standard over the last 50 years in the mining industry for battery-operated machinery was to match the voltage of the battery to the voltage rating of the motor. An engineer would receive information from the manufacturer of the motors and design batteries to fit the voltage of each motor based on the rated voltage of the motor.
Generally speaking, the rotational speed of a DC motor is proportional to the voltage applied to it, and the torque is proportional to the current. Torque and current are linearly proportional to each other, as are speed and voltage. Under a fixed load (torque) voltage and current will also be proportional to each other. The generated torque is dependent on the current (I) and factors determined by the materials and internal geometry of the motor. Since the construction of a finished motor will not change during operation, a constant proportionality between the motor current and the geometry dependent factors can be calculated for a given motor. This constant, the torque constant (Kt) describes the torque generated by the motor for a specific motor current.Kt=T/I  Eq. (1)
In other words, the current I through the motor equals the torque produced T divided by the torque constant Kt. Thus, the DC motor rotational speed is proportional to the voltage applied to it, and the torque is proportional to the current.
Battery vehicles in the underground mining industry have had ever increasing productivity demands while being constrained by the available battery power supply. The production of these vehicles is measured in tons carried per shift. This is significantly affected by how many hours of life the battery tray can provide without the need for recharging. Ideally, a battery should last an entire shift. However, this can be as long as 10 hours in some mines.
As the productivity demands increase, manufacturers have found it necessary to put larger amp-hour cells in their battery trays. Unfortunately, the selection of cells available from the battery manufacturers is limited to only a handful of distinct sizes, which are often difficult to fit into the existing spaces fitted on the vehicles. Thus, there is a desire for another method to increase the run time of these electric vehicles within existing space requirements.